Process for de-copperizing lead

ABSTRACT

LEAD CONTAINING A RESIDUAL SMALL AMOUNT OF COPPER IS DE-COPPERIZED BY A PROCESS INVOLVING ADDING CAUSTIC ALKALI TO THE COPPER-CONTAINING MOLTEN LEAD, ADDING PYRITE TO THE COPPER-CONTAINING MOLTEN LEAD, THE PYRITE BEING ADDED IN AN AMOUNT SUFFICIENT TO SUBSTANTIALLY REMOVE THE COPPER FROM THE LEAD, AND MIXING THE PYRITE AND THE CAUSTIC ALKALI WITH THE COPPER-CONTAINING MOLTEN LEAD. THE PYRITE AND CAUSTIC ALKALI ARE MAINTAINED MIXED WITH THE COPPER-CONTAINING MOLTEN LEAD AT LEAST UNTIL THE PYRITE REACTS WITH THE COPPER TO FORM A SULFUR COMPOUND OR COMPOUNDS OF COPPER. SUBSEQUENTLY A DROSS CONTAINING THE SULFUR COMPOUND OF COPPER IS SEPARATED FROM THE THUS-OBTAINED MOLTEN LEAD OF REDUCED COPPER CONTENT.

Sept. 26, 1972 Y. E. LEBEDEFF ErAL 3,694,191

PROCESS FOR DE-COPPERIZING LEAD Filed Sept. 11, 1970 SLAG To 8 melting A v REST DE-COPPER\Z\NG STAGE EECYCLE SLRG- 6 v LEAD OF REDUCED fCOPPE-LR CONTENT SECOND DECOPPER\Z\NG N0.0H STQGE PHRFFE DE*-COPPEE\ZED LEHD DESILNERIZING INVENTORS Wmuem C. KLElN YuRu E. LEBEDEFF United States Patent Oflice' 3,694,191 Patented Sept. 26, 1972 3,694,191 PROCESS FOR DE-COPPERIZING LEAD Yurii E. Lebedetf, Edison, and William C. Klein, Menlo Park, N.J., assignors to American Smelting and Refining Company, New York, N .Y.

Filed Sept. 11, 1970, Ser. No. 71,603

. Int. Cl. C22b 13/06 U.S. CI. 75-78 1 Claim ABSTRACT OF THE DISCLOSURE Lead containing a residual small amount of copper is de-copperized by a process involving adding caustic alkali to the copper-containing molten lead, adding pyrite to the copper-containing molten lead, the pyrite being added in an amount sufiicient to substantially remove the copper from the lead, and mixing the pyrite and the caustic alkali with the copper-containing molten lead. The pyrite and caustic alkali are maintained mixed with the copper-containing molten lead at least until the pyrite reacts with the copper to form a sulfur compound or compounds of copper. Subsequently a dross containing the sulfur compound of copper is separated from the thus-obtained molten lead of reduced copper content.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to a process for de-copperizing lead and more particularly to a new and improved process for the removal of relatively small or residual amounts of copper from lead.

(2) Description of the prior art Copper has been removed from lead heretofore by adding to the molten lead elemental sulfur alone, or in the presence of sodium hydroxide. The copper removal was accomplished by the formation of CuS, which is mineralogically known as covelite. Although the elemental sulfur was eflfective in removing the copper from lead, the use of the elemental sulfur in the presence or absence of an alkali metal hydroxide is disadvantageous from the standpoint of generating large amounts of obnoxious and harmful sulfur dioxide gas. Inasmuch as a number of state governments and the federal government are currently contemplating the enactment of regulations to compel a considerable reduction in an amount of pollutants including sulfur dioxide discharged into the atmosphere, the importance of avoiding discharge of considerable amounts of sulfur dioxide into the atmosphere is readily seen.

The removal from lead or lead alloys of any of the impurities arsenic, tin, zinc, selenium, tellurium, manganese, copper, iron, cobalt, cadmium, nickel and antimony, when present, by subjecting the molten lead or lead alloy to mixing with the mineral galena, i.e. lead sulfide, and molten caustic alkali is disclosed in U.S. Pat. 2,843,476 to Hoffman. The impurities, as far as they are present, are removed from the lead in the order stated supra, i.e., first arsenic, second tin, then zinc, etc. and the treatment with the galena and caustic alkali is carried out until the particular metal impurity intended to be removed is reached and removed. Thus to remove the copper from the lead, the treatment with the galena and caustic would be carried out to remove the arsenic, tin, zinc, selenium, tellurium and manganese, assuming all present and with the removal being in the order stated, and finally the copper. Of course the amount of lead sulfide used in that event would be at least the stoichiometric amount for removing the arsenic, tin, lead, zinc, selenium, tellurium, manganese and copper, with cessation of the removal operation after the copper is removed to the desired extent when a stoichiometric excess of lead sulfide is used. Although the metal impurities removal effected by the process of U.S. Pat. 2,843,476 may be satisfactory in many respects, the process of Pat. 2,843,- 476 would require the utilization of very large quantities of lead sulfide or galena reagent and exorbitantly large quantities of the caustic soda. The large requirements of galena and exorbitantly large requirements of caustic soda, especially the latter, would add considerably to the refining costs and are disadvantageous from an economic standpoint, and would undoubtedly render this prior process commercially unfeasible at least in this country. The process of U.S. Pat. 2,843,476 is also carried out at a relatively low temperature which may be as low as 300 C. and range up to only 350 C. or somewhat higher. However it would be desirable to carry out the de-copperizing at a materially higher temperature inasmuch as the desilvering operation, which follows the de-copperizing, is carried out with the lead at a considerably higher temperature than disclosed by Pat. 2,843,476.

U.S. Pat. 3,317,311 to Davey discloses a method for the rough copper drossing of lead and wherein elemental sulfur, lead-sulphides or iron-pyrites concentrates is added to the lead bullion as an agent for lowering the melting point of the matte. The use of the lead-sulphides or iron-pyrites concentrates is disclosed by Pat. 3,317,- 311 to be disadvantageous. Further, no caustic alkali is added to the lead. The rough copper drossing is effected in accordance with Pat. 3,317,311 by feeding the lead bullion into a vessel with an upper portion maintained at a sufiiciently high temperature to prevent any accretions' forming on the inside of its walls and a lower portion which is drastically cooled to form banks consisting of solid lead containing precipitated particles of impurities such as copper, or copper sulphides and arsenides, and drawing oif relatively cold drossed lead from the vessel bottom. From time to time the cooling of the vessel's lower portion is interrupted and the banks are melted 01f, whereby copper-containing particles float to the top of the lead in the vessel and dissolve in a molten matte layer. The molten matte layer is tapped ofi at intervals.

The removal of copper from lead by adding to the molten lead a sulfur-containing compound such as sodium sulfide, sodium polysulfide or sodium thiosulfate in the presence or absence of caustic alkali is also disclosed in the prior art.

To the best of our knowledge, the use of pyrite in conjunction with caustic alkali for removal from lead of residual small amounts of copper which remain after the rough copper drossing of the lead is not disclosed in the prior art and has never been employed in the prior art. Such residual small amounts of copper, unlike the relatively large amounts of copper which are removed in the rough copper drossing of the lead, are

ordinarily diflicult to remove from the lead down to the desired low level below 0.01% of copper.

SUMMARY OF THE INVENTION In accordance with the present invention, lead containing a small or residual amount of copper as an impurity is decopperized by a process comprising:

(A) Adding caustic alkali to the copper-containing molten lead;

-(B) Adding pyrite (Fes to the molten lead containing the small amount of copper in an amount sufiicient to substantially remove the copper from the lead;

(C) Mixing the pyrite and the caustic alkali with the copper-containing molten lead;

(D) Maintaining the pyrite and caustic alkali mixed with the copper-containing molten lead at least until the pyrite reacts with the copper to form a sulfur compound of copper, and

(E) Separating a slag or dross containing the sulfur compound of copper and located on the upper surface of the molten lead from the thus-obtained lead of reduced copper. content.

The instant process constitutes a considerable and meritorious improvement in the art by reasons of (l) eliminating completely the generation of obnoxious and harmful 80;, which is generated in large amounts when elemental sulfur is added to the molten lead alone or in the presence of caustic alkali; (2) requiring the addition of only very small amounts of caustic alkali and pyrite as compared to the exorbitantly very large and very large amounts of caustic alkali and galena respectively that are required by the prior art process utilizing galena as reagent in conjunction with caustic alkali; (3) being economical and a commercially feasible process due at least in part of (2); (4) greatly enhanced efliciency of sulfur utilization for copper removal due to the absence of sulfur burning and escaping as S gas; and (5) reducing the copper content of the lead to less than 0.008% and even to less than 0.005%, with the lead containing copper as sole impurities or containing other impurities in addition to copper. With regard (2) supra, the de-copperizing process of the present invention usually requires the addition of amounts of caustic alkali and pyrite to the molten lead which are considerably less than the amounts of caustic alkali and galena that would be required by the prior art process involving the utilization of galena in conjunction with the caustic alkali.

The process of this invention has de-copperized lead down to as little as 0.0025 of copper.

The pyrite can be FeS per se, or the pyrite can be present in a natural or synthetic material or a concentrate containing primarily pyrite, i.e. R28 The concentrate may also contain ferrous sulfide, i.e. FeS, in addition to other constituents and the primary constituent FeS .The lead which is treated in accordance with the present invention may contain copper as sole impurity, or it may contain additional impurities besides copper. Such additional impurities are, for example, one or more of silver, bismuth, arsenic, antimony and tin.

The mixing of the pyrite and caustic alkali with the impure molten lead containing the copper can be effected in any suitable manner. Thus any suitable mixer or stirrer, for instance an impeller-type mixer, can be employed for mixing the pyrite and caustic alkali together with the impure molten lead.

.The pyrite and caustic alkali are maintained mixed with the copper containing molten lead, ordinarily by continued mixing of such mixture, until the pyrite reacts with all or substantially all of the copper to form the sulfur compound or compounds of the copper thereby to remove the copper from the lead. The thus-formed sulfur compound or compounds of copper report in, i.e. are present in, a dross or slag that forms on the upper surface of the molten lead. The time for maintaining the pyrite and molten caustic alkali mixed with the impure molten lead until the pyrite reacts with all or substantially all of the copper is usually in the range of 1' /2-3- /2 hours. The dross, which is usually a dry, easily removable dross, is separated, usually by skimming, from the thus-obtained lead of reduced copper content.

The caustic alkali and pyrite can be added to the molten lead to be de-copperized in any sequence or together or a pre-mix. Thus, for instance, the pyrite can be added to the molten lead in the presence of the caustic alkali already present in the lead, the caustic alkali can be added first and then the pyrite, or the caustic alkali and pyrite can be added simultaneously as a pre-mix. The caustic alkali is preferably added first and subsequently the pyrite is added as in hereinafter disclosed.

The caustic alkali is NaOI-I or KOH, or a mixture of NaOH and KOH in any desired proportions.

The removal of the copper from the lead in accordance with the present invention can be effected utilizing a single de-copperizing treatment step or stage, or a plurality of de-copperizing treatment steps or stages, i.e. two or more de-copperizing steps or stages, with separation of a dross or slag containing the sulfur compound or compounds of copper from the lead in each stage.

The presence of the caustic alkali is critical in the process of the present invention for removal of the otherwise diificultly removable small residual amount of copper from the molten lead. The caustic alkali will usually be added to the molten lead in the instant process. However, in the event sufiicient residual caustic alkali is present in the molten lead from a previous metallurgical processing,

or is present in a slag or dross obtained from a previous or difierent de-coppering step or stage and which is utilized in or recycled to the particular de-copperizing step or stage, it may necessary to add additional caustic alkali to the lead melt for the de-copperizing at least in that particular stage or step, or it may only be necessary to add a portion only of the caustic alkali that would normally be required. In any event, the amount of caustic alkali utilized or present in the molten lead to be decopperized in accordance with this invention is a sufiicient amount thereof which, in conjunction with the pyrite, will result in removal of the copper from the lead to the degree or extent desired.

Although it is not known with certainty, one explanation advanced concerning the removal] of the copper from the lead in accordance with this invention is that the pyrite reacts with the copper in the presence of the caustic alkali to form CulFeS as the primary sulfur compound of copper among a plurality of such compounds. The CuFeS which is mineralogically known as chalcopyrite, exhibits a large thermal stability, thereby permitting the utilization of higher temperatures which may range up to 850 F. and even higher. However other sulfur compounds or sulfur compound of copper that may be formed to the partial or complete exclusion of the g uges are exemplified by chalcocite, Cu S, and covellite,

The slag or dross from a previous or different de-copperizing step or stage and which contains residual caustic alkali and usually also contains residual pyrite, a sulfur compound or compounds of copper, and lead, may if desired be utilized in or recycled to the de-copperizing step or stage for addition to the molten lead.

Good results have been achieved in de-copperizing lead bullion in accordance with this invention by utilizing the pyrite and caustic alkali in minor amounts within the ranges of from about 0.l0%0.25% of the pyrite and from about 0.13%-0.3*0% of the caustic alkali, the percentages being by weight and based on the molten lead charge.

Certain materials such as an alkali 'metal chloride, e.g. sodium or potassium chloride, an alkali metal carbonate, e.g. sodium or potassium carbonate, and/or borax may be added in minor amount to the dross or slag on the molten lead bullion. These additions are beneficial from the standpoint of maintaining a desirably fluid dross or slag on the bullion surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferably the caustic alkali is added to the molten lead first and then the pyrite is added.

The copper is contained in the molten lead bullion to be de-copperized in a small but perceptible amount preferably not more than 0.1% by weight, more preferably from about 0.02% to 0.1% by weight inclusive.

The weight ratio of caustic alkali to pyrite utilized in this invention is preferably about 1.301.6:1 respectively.

The temperature of the molten lead to be de-copperized in accordance with this invention is preferably at a temperature in the range from about 640 F. to about 850 F., more preferably from about 640 F. to about 720 F., and most preferably from about 690 F. to about 720 F. At higher temperatures of the molten lead much above 850 F., the efficiency for copper removal decreases. Temperatures of the molten lead much below 640 F. are disadvantageous by reason of the alkali slag drying and causing entrapment of bullion.

The pyrite or material or concentrate containing it is preferably in finely divided state when added to the molten lead. Typical particle size of the finely divided material or concentrate is 99% through a 35 mesh sieve, 43% through a 100 mesh sieve and 18% through a 200 mesh sieve.

The mixing of the pyrite and .caustic alkali with the copper-containing molten lead is preferably effected by stirring the molten lead containing the added pyrite and caustic alkali in such a manner as to produce a pronounced vortex in the molten lead. A conventional motordriven impeller-type mixer has been used to produce such vortex with good results.

DETAILED DESCRIPTION OF THE DRAWING Referring now to the drawing the single figure of which illustrates a flow sheet of the most preferred embodiment, molten lead bullion containing typically about 0.04% of copper, about 0.02% of silver, and perhaps bismuth, antimony, arsenic and tellurium in small amounts typically less than 0.01% of each and obtained from a conventional lead softening operation or another metallurgical operation with respect to the lead is contained in ladle 5. The molten bullion was charged at a temperature of about 700 F. into a kettle of a first de-copperizing step or stage 6 in a kettle and the bullion and slag mixed being 245 tons. A recycle slag or dross from a second de-copperizing step or stage hereinafter disclosed was added to the molten bullion in the first de-copperizing step or stage 6 in a kettle and the bullion and slag mixed together therein for l%1% hours therein by means of a suitable mixer to produce a pronounced vortex in the molten bullion. The recycle slag contains residual caustic alkali such as NaOH, residual pyrite, lead, and copper as a sulfur compound or compounds of copper. A desirable dry, readily removable slag or dross is formed on the upper surface of the molten bullion and is skimmed off the bullion surface and conducted to a smelting operation, for metal values recovery. The copper content of the molten lead after the first de-copperizing step 6 averaged 0.028% copper. The average weight of the slag skimmed from the bullion in the first copper removal stage was about 1 ton per each 245 ton charge of molten bullion to the kettle. Such slag or dross contained lead, copper, iron, sulfur, and caustic alkali with the sulfur being chemically combined with the copper as the sulfur compound or compounds of copper.

Caustic alkali such as NaOH and pyrite were then added to the molten lead of reduced copper content from the first de-copperizing stage in a second de-copperizing step or stage 7 in a kettle, which is ordinarily the same kettle as utilized for the first de-copperizing stage 6 with the molten lead simply being retained in the same kettle for the second de-copperizing step 7. Although the molten lead is ordinarily retained in the same kettle during the first and second decopperizing steps as pointed out supra, if desired, separate kettles may be utilized for the first and second de-copperizing steps or stages. NaOH and pyrite were added to the molten lead in the second stage 7 in amounts of about 0.15% and 0.11% respectively, the percentages being by weight and based on the weight of the molten lead charge. The molten lead was at a temperature of about 700 F. for the second de-copperizing step 7. The pyrite and NaOH were mixed together with the molten lead in the kettle and maintained mixed together with the molten lead therein for a time in the range of 1 A-3 hours, which was sufficient for the pyrite to react with substantially all of the copper to form the sulfur compound or compounds of the copper, by means of a suitable mixer to produce a pronounced vortex in the molten bullion. The slag or dross that formed on the upper surface of the molten bullion in the second step 7 and which contains the thus-formed sulfur compound or sulfur compounds of copper was skimmed off, and returned for addition as the aforementioned recycle slag or dross to a newly-incoming batch charge of molten bullion to be de-copperized in the first de-copperizing stage 6.

The copper content of the lead from the second decopperizing step averaged 0.005%.

The de-copperized molten lead from the second decopperizing step 7 may then be passed to a de-silverizing operation.

The de-copperizing process herein is free or substantially free of S0 generation.

The following examples further illustrate the inventron:

Fifty-six (56) charges of molten lead bullion were decopperized. Each molten lead charge to the kettle was 245 tons, the temperature of the molten lead of each charge during the de-copperizing was about 700 F., the average amount of pyrite (FeS used was 550 lbs. per 245 ton charge (equivalent to about 0.11% of pyrite based on the lead charge), the average amount of NaOH used was 780 lbs. per 245 ton charge (equivalent to about 0.15 of NaOH based on the lead charge), and the average NaOH/pyrite ratio was 1.4. The average mixing and skimming time for the two step de-copperizing treatment was 2 /23- /2 hours, not counting cooling time. The decopperizing of the lead bullion was a two stage de-copperizing with the molten slag skimmed from the bullion 1n the second de-copperizing or treatment stage of one 1 example being returned to the kettle for use in the first treatment stage of the next example. The average copper content of the molten lead before de-copperizing was 0.042%. The average weight of the slag produced per 245 ton charge was 2064 pounds, and the average calculated copper content of the slag was 9.9%. The pyrite utilized for each charge was a pyrite concentrate containmg, by weight, 50.0% sulfur, 42.8% iron, 0.25% copper, 0.25 lead, 1.00% zinc, 0.05% arsenic, 0.01% selenium, 0.01% tellurium, 0.05 phosphorus and 7.0% insolubles. The pyrite concentrate was in finely divided state and of a screen size such that 99% of the concentrate passed through a 35 mesh sieve, 43% through a 100 mesh sieve, and 18% through a 200 mesh sieve. The metallurgical data obtained in de-copperizing the 56 charges is set forth hereafter in Table I.

TABLE I The good results in de-copperizing the Pb to low levels Cu content of Finawuwntent of Cu is shown by the data of Table I. In Example I C bu l o Mtg igg (Charge) 43, the Cu content of the lead was reduced to 111 131 11 I881 mg W1 rea ExampleN 00110331; in recycled 513% NaOH 466 11 the low level of 0.002%, in Examples (Charges) 19 and (charge) 0 b (W ,0 37 to the low level of 0.003% Cu, and 1n all the examples 8:828 818%? 818 2 (Charges) the Cu content of the lead was reduced to the 8-8:: 8- 8888 average low level of 0.005% Cu. The symbol w./o. in 3-82: 3838 8-888 10 the two columns of Table I mean weight percent. giggg 8.8%? 8-86; Twenty-six (26) charges of molten lead bullion were 0:032 0:031 818%; de-copperized utilizing pyrite in conjunction with caustic 1182; 013%; 01005 alkali (NaOH) and a procedure similar to that utilized 8:888 8:828 8:882 for the 56 charges of molten bullion of the examples 888g 8: 888 8888 set forth previously herein in Table I, the results of the de- M05 copperizin of the 26 char es being set forth here- 0.042 0:040 0.008 g 3.8%? 8-821 3-332 after 1n Table II. However 1n the case of the 26 charges 0:040 01 026 813%: reported in Table II, the slag was not recycled as was 0.0 4 8823 3 0. 009 done in the examples for the first-ment1oned 5'6 bullion 8:83? 88%; 3 38; charges except that in the case of Examples No. 61, 63 88g 8888 8:888 and 74 the slag or dross was returned to the charges along 8-823 8-85 888? with a portion of the NaOH and FeS The results of the 8:82? 8-833 3-832 de-copperizing are set forth in Table II, below. 01025 01019 8:88: The data of Table II shows de-copperizing of the lead 0. 8.822 0.837 3. bulllon by the process of th1s 1nvent1on to low copper 0.05 0.050 8 8 883% 3882 levels as low as .003% Cu (Example 79), and to an .044 I 060 052 003 average low level of 0.008% Cu. 3-8;? 3-832 8-88: In Examples No. 60, '62, and 73 of Table II, below, 81 8.8%: 3-3 61 dross was skimmed wet from the molten bullion in 0:029 0:023 82% each case and a portion of such dross was returned to 0.004 8.2%; 0.025 0.003 the bullion charge of Examples No. 61, 63 and 74 re- 882 8:888 8:888 spectively along with the amounts of NaOH and pyrite 8:83 8:888 8:888 enumericated for Examples No. 61,- 63 and 74. A two 6.033 0.029 0.004 0.026 0 009 0.003 stage de copperizlng was earned out in Examples 61 and 0.036 3. 3. 3, 0. 030 0. 037 0. 027 2 Tests were carried out to determine the efl'ect the ram 0.022 8 8%; M58 0,005 of caustic alkah to pynte had in the de-copperlzing of 051 N34 N03 lead. The molten lead treated in each test contained 0.06% of copper. The test results follow in Table III.

TABLE 11 Cu content :3 er Final liquidation Cu content (percent (percent NaOH Pyrite Example No. by weight) by Weight) (lbs.) (lbs.) Time, hrs. Temp., F.-

TAB LE III Percent Cu in lead after specified Ratio, period of mixing Dross emp Caustic Pyrite caustic produced Example No. (lbs/ton) (lbs./ton) pyrite min. min. min. (lbs/ton) The test results of Table III and specifically thosevof Example Nos. 85 and 85 compared with the test results of the remaining Example Nos. 83, 84, 87, 88 and 89 show that a weight ratio of caustic alkali to pyrite of 1.291.57: 1 respectively added to the molten lead to be de-copperized resulted in reducing the copper content of the lead to a level below 0.01%, and specifically to 0.0035 and 0.006% respectively. Although Example No. 89 effected de-copperizing to 0.005% copper in the lead, Example No. 89 required appreciably more caustic and pyrite than was employed in Example No. 85 and appreciably more pyrite than was employed in Example N0. 86. Further Example No. 89 produced about three times or more dross than was produced in Examples Nos. 85 and 86.

What is claimed is:

1. A process for de-copperizing lead containing a small amount not more than 0.1% by weight copper without generating any S0 which comprises:

(a) adding caustic alkali to copper-containing molten lead containing not more than 0.1% copper at a temperature in the range from about 640 F. to about 720 F.;

(b) adding pyrite to the copper-containing molten lead containing not more than 0.1% copper at a temperature within the aforesaid range, the caustic alkali and pyrite being added in amounts suflicient to result in removal of the copper from the lead;

(c) mixing the pyrite and the caustic alkali with the copper-containing molten lead at a temperature in the range from about 640 F. to about 720 F.;

(d) maintaining the pyrite and caustic alkali mixed with the copper-containing molten lead until the pyrite reacts with the copper to form at least one sulfur compound of copper;

(e) the thus-formed sulfur compound of copper reporting in a readily removable, caustic alkali-containing dross formed on the upper surface of the molten lead thereby resulting in lead of a reduced copper content; and (f) separating the dross containing the sulfur compound of copper from the thus-obtained lead of reduced copper content; (g) lead containing less than 0.008% copper being obtained in the process; (h) the process being carried out without generation of any S0 References Cited UNITED STATES PATENTS 1,025,956 5/1912 Asbeck 78 2,543,041 2/1951 Meyer 7578 2,843,476 7/1958 Hoffman 7578 2,109,144 2/ 1938 Betterton et al 7578 1,386,503 8/ 1921 Hulst et al 7578 1,582,037 4/1926 Harris 7578 2,217,981 10/ 1940 Hallows 7578 FOREIGN PATENTS 925,822 5/1963 Great Britain 7578 1,102,971 2/ 1968 Great Britain 7578 1,104,596 2/1968 Great Britain 7578 HERBERT T. CARTER, Primary Examiner US. Cl. X.R. 75-79 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pa en 3,694,191 I Dated September 26,1972

Inventor(s) Yulii E Lebedeff e1; 8.1

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column'3, line 36, "of", first occurrence, should read to Column 4, line 8, "or", second occurrence, should read as line 15, "in" should read is line 35 not should be inserted after "may" and before "necessary". Column 5, line 54 "in a kettle and the bullion and slag mixed" should be deleted; line 54, the phrase with a typical bullion charge to the kettle should be inserted immediately after "6" Column 7, in TABLE I the horizontal line thereof corresponding to "Example [charge] No 44",

"0 .025" should read 0 .024

Signed and sealed this 8th day of May 1973 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM POWSO USCOMM-DC 60376-P69 Y [1.5. GOVERNMENT PRINTING OFFICE: [959 0-355-33L 

